In the process of conducting coring operations within an oil or gas wellbore, a coring tool is run downhole by wireline conveyance and multiple core samples are cut from the wellbore. The core samples are placed within a pressure vessel in the wellbore. The pressure vessel is then sealed downhole with a plug that retains the recovered core samples and fluids during recovery of the pressure vessel to the surface. The core samples are subsequently shipped offsite for detailed laboratory analysis. The sealed pressure vessel containing the core samples cannot be opened outside of the laboratory without risking adverse effects on the quality and integrity of the core samples. Further, the use of certain implements to determine the volume of the core samples within the pressure vessel such as, for example, X-ray machines and/or CT scan machines, is often precluded by the design and construction of the pressure vessel itself. As a result, the volume of the core samples within the pressure vessel recovered from the wellbore is often unknown before the pressure vessel is opened in the laboratory. Thus, the volume of the core samples within the pressure vessel typically cannot be determined until after the necessary coring equipment and personnel have left the wellsite. Accordingly, a method for determining the volume of the core samples within the pressure vessel at the wellsite would allow for additional coring operations to be conducted, if necessary, while the required equipment and personnel are still available at the wellsite.